1. Field of the Invention
The present invention relates to a process for manufacturing a sheet stack in which sheets of wet tissue paper, wet nonwoven fabric, dry tissue paper or dry nonwoven fabric are so stacked in a folded state that they can be sequentially taken out.
2. Related Art
Wet sheets for wiping hands or anal regions of babies or for cleaning toilets or dining rooms are sealed and accommodated in a packaging member such as a hard container or a bag formed of a packaging sheet, so that they be kept in the wet state. In this packaging member, moreover, there is formed an opening for allowing the sheets to be sequentially taken out. The wet sheets of this kind are combined with the upper and lower ones being connected to each other. When the upper sheet is pulled out of the opening, the lower sheet is dragged by the upper sheet so that an upper portion of the lower sheet may be protruded from the opening.
Examples of the so-called xe2x80x9cpop-up type sheet stackxe2x80x9d of this kind in the related art are shown in FIGS. 12 and 13.
In a sheet stack 1 shown in FIG. 12, each sheet 2 of a predetermined width is folded in two to have a v-folded structure in which an upper fold is designated by 3 and a lower fold is designated by 4. Between the upper fold 3 and the lower fold 4 of one sheet, moreover, there are sandwiched the lower fold 4 of the overlying sheet and the upper fold 3 of the underlying sheet. Between upper and lower sheets, the upper fold 3 and the lower fold 4 are joined (closely contacted) with each other at an overlap portion of a predetermined width La.
In a sheet stack 5 shown in FIG. 13, each sheet 6 of a predetermined width is folded in three to have a z-folded structure in which an intermediate fold is designated by 7, an upper fold folded back upwardly from the intermediate fold 7 is designated by 8 and a lower fold folded back downwardly from the intermediate fold 7 is designated by 9. Over the lower fold 9 of one sheet, there is laid the upper fold 8 of the underlying sheet. These lower fold 9 and upper fold 8 are joined (closely contacted) with each other at an overlap portion of a predetermined width Lb.
The sheet stacks 1 and 5 are individually accommodated in a packaging member such as a hard container of plastics or a bag formed of a soft packaging sheet. As one sheet is taken out from the opening formed in the upper face of the packaging member, the next sheet overlapping with that overlap portion is pulled out so that its end portion is partially protruded from the opening, after the upper sheet was taken out, and is allowed to be subsequently taken out.
The sheet stacks 1 and 5 can be manufactured as follows: At first, band sheets are continuously unwound from individual roll goods in a number corresponding to the number of the sheets to be stacked. Then, by using a guide plate, each band sheet is folded along a longitudinal direction (flow direction) thereof into the v-folded structure shown in FIG. 12 or into the z-folded structure shown in FIG. 13. Simultaneously with this v-folding or z-folding step, upper and lower sheets are so combined as to overlap each other with the aforementioned overlap portion. As the aforementioned steps are performed for every band sheets, there is formed a band-shaped sheet stack in which band sheets are folded and combined as shown in FIG. 12 or FIG. 13. This band-shaped sheet stack is cut to a predetermined length to manufacture the individual sheet stacks. This sheet stack is impregnated with a liquid into a wet state and is packaged in the packaging bag.
In the case where each sheet is folded once into such a v-folded sheet as shown in FIG. 12 or folded twice into such a z-folded sheet as shown in FIG. 13, the folding number of each sheet is so small that it is possible to combine upper and lower sheets simultaneously with the folding of the lower sheet such that a portion of the upper sheet is sandwiched between folds of the lower sheet.
However, if an original entire width (i.e., width before folded) of the sheet is 190 mm or 200 mm and if the width La or Lb of the overlap portion is set at 30 mm most preferable for the stack of the wet sheets, for example, the width of the sheet stack 1 or 5 becomes too large. In the case where the v-folded sheets are combined as shown in FIG. 12, the sheet stack has a width of about 170 mm. In case where the z-folded sheets are combined as shown in FIG. 13, on the other hand, the sheet stack has a width of about 85 mm. Accordingly, it is difficult to accommodate the sheet stack in a small-sized packaging member suitable for potable use, for example.
In order to provide a sheet stack having a smaller width from the sheets having the original width of 190 mm or 200 mm, therefore, it is necessary to increase the folding number of the individual sheets. However, when each sheet is to be folded along three or more fold lines into a sheet folding structure having four or more layers, it becomes difficult to adopt the aforementioned folding step, at which upper and lower sheets are combined simultaneously with the folding of the lower sheet. When each sheet is to be folded into four or more layers and the upper and lower sheets are to be combined simultaneously with this folding, more specifically, the structure of the guide plate (generally called xe2x80x9csailorxe2x80x9d) is extremely complicated. Even if this folding should be possible, on the other hand, the precision of the folding width would be difficult to keep.
In order to avoid the foregoing problems while folding each sheet in a large folding number and combining the upper and lower sheets, for example, Japanese Unexamined Patent Publication No. Heisei 10-174663 (174663/1998) discloses a folding process in which a band sheet is folded along a longitudinal direction (flow direction) thereof and is then folded back along a direction perpendicular to the longitudinal direction thereby to increase the folding number. However, if the sheet is folded back in the direction perpendicular to the flow direction, the flow velocity of the sheet for forming the sheet stack is difficult to speed up with a resultant defect that the mass productivity is lowered.
The present invention has been worked out in view of the problems set forth above. An object of the present invention is to provide a sheet stack manufacturing process for manufacturing a compact sheet stack in a high mass productivity.
According to the invention, there is provided a sheet stack manufacturing process comprising:
feeding a plurality of band sheets;
folding each band sheet at least once along a longitudinal direction thereof at a first folding step, to form folded bands;
folding each folded band along the longitudinal direction at a second folding step to have at least three fold lines by the first and second folding steps and to sandwich a portion of at least one of an overlying sheet and an underlying sheet thereof, thereby to form a band-shaped sheet stack in which a plurality of sheets are combined with one another so as to be stacked on one another; and
cutting the band-shaped sheet stack to a predetermined length to be separated into individual sheet stacks.
For example, at the first folding step, each band sheet may be folded only once into a two-folded band having upper and lower folds, and at the second folding step, the upper and lower folds of each two-folded band may be folded together in one direction so as to sandwich a portion of at least one of an overlying sheet and an underlying sheet thereof.
In an alternative, at the first folding step, each band sheet may be folded only once into a two-folded band having upper and lower folds, and at the second folding step, the upper and lower folds of each two-folded band may be folded in opposite directions so as to sandwich a portion of an overlying sheet thereof with folding of the upper fold at the second folding step and sandwich a portion of an underlying sheet thereof with folding of the lower fold at the second folding step.
In another alternative, at the first folding step, each band sheet may be folded twice into a three-folded band, and at the second folding step, a portion of each three-folded band may be folded so as to sandwich a portion of at least one of an overlying sheet and an underlying sheet thereof.
In the sheet stack, preferably, all the sheets are subjected to the first and second folding steps and folding structures are symmetric between upper and lower sheets.
As set forth, the individual band sheets are folded into the folded bands at the first folding step prior to the second folding step. Then, the individual folded bands are fed to the second folding step and further folded to be combined with another sheet. Therefore, it is possible to make such a complicated folding structure as has never been practiced in the related art. In this folding structure, for example, four or more folds are overlapped in the thickness direction, and the upper and lower sheets are combined. In addition, since all the fold lines extend in the longitudinal direction (flow direction) of the band sheet, the manufacture line can be speeded up.
Here, it is also possible that other band sheets, as fed without being subjected to the first folding step, are folded simultaneously with the second folding step to have at most two fold lines and to be combined with the folded bands subjected to the first and second folding steps so that folding structures are different between upper and lower sheets in the sheet stack.